Spherulitic morphologies of a series of linear poly(Llactide)s (PLLA)

which was synthesized by ring opening polymerization (ROP) using initiators with different structures

i.e.the incoming end groups

were observed through direct meltcrystallization process by polarized optical microscopy (POM).It has been verified that the flexibility of the end group has a significant influence on the banded structure of PLLA spherulites.It was found that the spherulitic band spacing periodicity of PLLA initiated by rigid benzyl alcohol (BPLLA) was much smaller than that of PLLA initiated by flexible lauryl amine (L-PLLA) with similar molecular weight at certain crystallization temperature.However

this end group effect was decreasing with increasing molecular weight.For B-PLLAs

the band spacing periodicity of spherulites increased with molecular weight increasing noticeably

for example

B-PLLA1 having a molecular weight of about 1700 yielded spherulites with band spacing periodicity being only several micrometers and spherulites of B-PLLA4 having a molecular weight of about 7000 had the band spacing periodicity more than 150 micrometers.Meanwhile

the temperature windows for the formation of regular banded spherulites of B-PLLAs shifted to higher region and became narrower with increasing molecular weight.Finally

a model was suggested to illustrate the effects of end group and molecular weight on the formation of twisting PLLA lamellae.